1. Field of the Invention
The present invention relates to wireline logging systems for subsurface resource drilling, and more particularly relates to providing power for wireline logging.
2. Related Art
The exploration for subsurface resources such as hydrocarbons including oil and gas, minerals and water, typically requires various techniques for determining the characteristics of geological formations. Many characteristics, such as the hydrocarbon volume, resistivity, porosity, lithology, and permeability of a formation, may be deduced from certain measurable quantities associated with the geological formations. It is a well-known technique to measure these characteristics by drilling a well in conjunction with a wireline logging system.
Wireline logging generally refers to the surveying and operation of wells by using various tools and electronic measuring instruments conveyed into a wellbore with an armored steel cable, commonly referred to as a wireline cable. Wireline logging systems generally refers to the tools and techniques utilized in the surveying and operation of wells. Various aspects of the wireline logging systems are described in the following U.S. Patents, which are incorporated herein by reference: Telemetry System For Borehole Logging Tools (U.S. Pat. No. 6,552,665), Power Source Regulator For Wireline Cable System (U.S. Pat. No. 6,522,119), and Wireline Cable (U.S. Pat. No. 6,297,455).
Measurements are made by downhole instruments, which are secured to the wireline cable. The measurements are transmitted from the instruments to a computer system located at the surface through multiple electrical conductors included within the wireline cable. Various wireline logging tools based on electrical, acoustical, nuclear, magnetic and imaging technologies are used to stimulate the geological formations and/or fluids within the wellbore and the electronic measuring instruments then measure the response of the geological formations and/or fluids. In addition to providing structural support for conveying the tools and measuring instruments into the wellbore, and for communicating the measurements to the surface based logging devices, the wireline cable is also used to provide electrical power to these various logging tools and measuring instruments.
The power requirements for the individual logging tools and measuring instruments may vary from a few watts to about 3 kilowatts. The specific types of voltage and/or current signals (or waveforms) used to provide the power may vary from direct current (DC) to alternating current (AC). The DC voltage signal may vary from 0 Volts to 2,000 Volts. The AC voltage signal may vary from 0 to 1,100 Volts. The AC current signal may vary from 0 Amperes (Amps) to 10 AmpsRMS. Depending on the number and types of logging tools and measurement devices used, the cumulative power requirement may vary from 500 Watts to about 10 kilowatts.
Traditionally, the above described power signals are generated by a variety of disparate tools and techniques depending on the nature of the output required, as described in FIG. 1. For example, an AC input power 110 may be derived from the power utility network or from an on-board electrical generator set. The AC input power 110 may be single phase or 3 phase. A fixed or adjustable transformer 120 (the adjustable or variable transformer is also referred to as a variac) may be used to change the output voltage. The output frequency, however, remains the same as the input frequency. Transformers may be used to multiplex power circuits by tapping the center of the secondary. Automatic control may be achieved by connecting a stepper motor to the variac axis of a transformer 130.
A high power DC generator 112 may include the above fixed and variable transformer combination in association with a rectifier and filter (not shown). The high power DC generator 112 may be used to generate a DC current signal 105, although more modern systems take advantage of switching programmable converters. For example, the following U.S. patent describes various aspects of using programmable switching power supplies and is incorporated herein by reference: High-Power Well Logging Method And Apparatus (U.S. Pat. No. 6,469,636). A waveform generator 115 may be used to obtain a very low frequency current signal 125 required for geological measurements. A motor-generator set 135 may be used to generate a 120 Hertz AC power signal 145, which may be required in some wireline logging systems.
Currently, a traditional wireline logging system may include a number of the above-described types of generators with each type of generator providing a particular type of output signal. A traditional power supply system, which provides power to the tools and instruments through a logging cable 150, is configured by assembling various types of disparate individual generators. The armor cable 152, which is included in the logging cable 150 provides structural support and is used as a ground. The specific size and type of generator selected is based on power requirements defined by the particular tools and instruments (not shown) used for wireline logging. The generators may be connected between themselves and to a power distribution system 160. The power distribution system delivers the power to the tools and instruments through multiple conductors 155 included in the wireline cable 150. The traditional approach to providing power thus results in cumbersome and bulky power supply systems having different types of power sources to manage and maintain. Spare parts requirement to stock the disparate types of generators increase asset costs. Designing for redundancy to accommodate failures further adds to the costs and size.
It should therefore be appreciated that a need exists to provide a power supply module included in a wireline logging system, in which the power supply module is operable to generate AC or DC power having customized voltage and current waveforms. Furthermore, it would be desirable to build complex power supply systems for wireline logging using the power supply module as a basic building block. For example, it would be desirable to build a power supply system having a modular architecture from a plurality of the power supply modules such that the power supply system is scalable to match the power, voltage, current, cost, spare parts, and reliability requirements of the wireline logging system application.